Footage of a so-called smoke explosion enveloping firefighters within seconds in Sunnyside, Queens, was additionally shocking because no one was killed.

Thick smoke from a still-young fire, which had billowed above an entire city block early Thursday morning in Sunnyside, Queens, suddenly, and ominously, was sucked back inside.

It was a telltale sign to firefighters of what was about to happen, and what they could not avoid.

A firefighter hastily put on his helmet, a half-second before the flash. The smoke then exploded into a fireball that catapulted across the street and simultaneously enveloped seven firefighters in a black curtain of dread.

Except, when the smoke cleared, they were all still standing. Alive.

"We have a bit of a miracle here," New York Fire Department Commissioner Daniel A. Nigro said. And videos of the explosion to prove it were shared on social media.

Footage of the so-called smoke explosion, more commonly known as a backdraft, stunned New Yorkers Thursday morning with its dramatic power and its even more shocking result: only 12 minor injuries, seven firefighters and five civilians. By the morning, the Fire Department said it had been contained.

The combustion happened when oxygen met extreme heat contained in a common loft space beneath the roof connecting the businesses on the block, which firefighters call a "cockloft." The explosion that followed the backdraft made the fire, in firefighting parlance, "run."

On the sidewalk, the members of the fire department were likely shielded by their bunker pants, hoods and helmets, Commissioner Nigro said.

Officials were notified of the fire at 2:14 a.m. More than 200 firefighters responded, and a total of 44 units raced to the scene. The fire occurred between 45th and 46th Streets on Queens Boulevard and originated in a diner known as New York Style Eats, officials said. The cause, said Commissioner Nigro, was still under investigation.

The block had stood since 1931, its immigrant-owned small businesses emblematic of the changing ethnic diversity of Queens.

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Humberto Sanchez, 26, said he was awakened by the smell of smoke from a block away. Fearing his building was on fire he ran outside to Queens Boulevard, and then walked closer to the scene out of curiosity. That's when he saw the roof of Sidetracks collapse, instantly sending out a blast of horizontal smoke and debris.

"There was this big, black explosion coming at me," he said at the scene later on Thursday. "People were shouting, 'Oh my god,' the street got filled up with smoke, I thought something blew up. It was pretty scary, I'm not gonna lie."

Lena Lam, 59, manager of the UPS store that was burned, was trembling while standing on the sidewalk Thursday morning, from either cold or shock or both.

Azure Chunton, 15, worked a shift for his uncle, the owner of Zen Yai, on Wednesday night. He said that there had been complaints that employees from New York Style Eats had dumped vats of cooking grease into the back alley.

"Yesterday it was like this oil and garbage everywhere," he said

Romantic Depot, a franchise of an erotica store catering to couples, opened at the end of October on the corner in a former Radio Shack. Neighbors were not pleased.

Jairo Ruiz, 59, said he had peeked in the store with his wife about two weeks ago and had an immediate impression.

"I said, 'This is a hugely flammable place,'" he said. "Because a lot of stuff is synthetic, the cheapest plastic, you can tell when stuff is made very cheaply."

He added: "It was like a perfect storm."

Behind it, on the 45th Street side, was Better Line Hardware.

A man who identified himself as the owner said he feared he had lost his longstanding connection to the community.

"I know everybody here," said the man, who did not wish to give his name. "The sentiment is you know everybody for 30 years, you see them as babies to grown-ups to be married."

State Senator Michael Gianaris, a Democrat representing Sunnyside, said he would help the businesses rebuild. "Sunnyside is a thriving community of small businesses and we cherish that, especially in an era where the big, giant operations are coming," Mr. Gianaris said. "That stretch of Sunnyside was a great success story for small businesses, and losing some of our most important ones, at least temporarily, is a body blow."